1. Field of the Invention
This invention relates to a transmission electronic control unit for controlling the operation of a transmission installed in a vehicle.
2. Description of the Related Art
As a transmission being installed in a vehicle for converting the rotation speed of an output shaft of an engine into various rotation speeds to smooth running of the vehicle, automatic transmissions compatible with vehicles called automatic cars have been mostly used in place of conventional manual transmissions. The automatic transmission is provided with a transmission electronic control unit (ECU) for controlling the automatic transmission operation of the automatic transmission.
A transmission installed in a vehicle is placed in the proximity of an engine in an engine compartment in which the engine is housed. However, formerly the transmission ECU was placed in a cabin of a kind of living space for passengers in a state in which the transmission ECU was at a distance from the transmission. In recent years, the installation locations of the transmission ECU and other ECUs have been changed to an engine compartment because of demands for enlarging the cabin volume intended for improving the comfort of the cabin and optimization of in-cabin placement of an audio machine, a navigation system, etc.
Since the transmission ECU and other ECUs use various semiconductor parts, the endurance assurance temperature is about 125xc2x0 C. to 150xc2x0 C. When the transmission ECU is placed in the cabin as ever, the environmental temperature to which the transmission ECU is exposed is about 80xc2x0 C. at the maximum. Therefore, if temperature rise caused by self-heating as the transmission ECU operates is added, the temperature of the transmission ECU does not reach 125xc2x0 C. to 150xc2x0 C., the endurance assurance temperature mentioned above, and there is no fear of damage to the semiconductor parts contained in the transmission ECU.
However, when the transmission ECU is placed in the engine compartment, the temperature in the engine compartment becomes 120xc2x0 C. to 150xc2x0 C. because of heat generated by the engine. Thus, if temperature rise caused by self-heating as the transmission ECU operates is further added, the temperature of the transmission ECU exceeds the endurance assurance temperature and damage to the semiconductor parts occurs; this is a problem.
To solve the problem as described above, for example, JP-A-10-166965 and JP-UM-A-6-4461 disclose related arts for suppressing the temperature rise of the transmission ECU. In these publications, the temperature of a transmission ECU or the temperature having a correlation with the temperature of the transmission ECU is detected and when the detected temperature is equal to or greater than a predetermined temperature, power supply or a part of power supply to the transmission ECU is shut off for stopping the operation of the transmission ECU, thereby suppressing self-heating of the transmission ECU.
In the publications, however, the power supply is shut off simply based on the temperature of the transmission ECU independently of the run state of the vehicle, namely, the operation state of the transmission. Therefore, it is feared that even evacuation running of the vehicle will be made impossible.
It is an object of the invention to provide a transmission electronic control unit capable of controlling self-heating in response to the operation state of a transmission and suppressing a temperature rise.
According to a first aspect of the invention, a transmission electronic control unit is installed in a vehicle for controlling operation of a transmission installed in the vehicle. The transmission electronic control unit includes a pulse width control section, a constant current control section, and an energization control section. The pulse width control section performs pulse width control of a current flown into a drive circuit for operating the transmission. The constant current control section controls the current flown into the drive circuit for operating the transmission to a constant value. The energization control section performs switch control between the operation of the constant current control section and the operation of the pulse width control section so that the constant current control section energizes the drive circuit when the operation of the transmission is placed in a constant state and that the pulse width control section energizes the drive circuit when the operation of the transmission is not placed in the constant state.
In the first aspect of the invention, the energization control section performs switch control so that the constant current control section energizes the drive circuit for operating the transmission when the operation of the transmission is placed in the constant state and that the pulse width control section energizes the drive circuit when the operation of the transmission is not placed in the constant state. Accordingly, heat generation in the transmission electronic control unit (ECU) is distributed between heat generation of the pulse width control section and heat generation of the constant current control section in response to the operation state of the transmission, so that the self-heating value of the transmission ECU is suppressed. Therefore, if the transmission ECU is placed in an engine compartment, the temperature does not exceed the assurance temperature and thus damage to the semiconductor parts, etc., placed in the transmission ECU is prevented.
According to a second aspect of the invention, a transmission electronic control unit is installed in a vehicle for controlling operation of a transmission installed in the vehicle. The transmission electronic control unit includes a pulse width control section and an energization control section. The pulse width control section performs pulse width control of a current flown into a drive circuit for operating the transmission. The energization control section controls the operation of the pulse width control section so that a pulse period (T1) of the current flown into the drive circuit when the operation of the transmission is placed in a constant state becomes larger than that (T2) of the current flown into the drive circuit when the operation of the transmission is not placed in the constant state.
In the second aspect of the invention, the energization control section controls the operation of the pulse width control section so that as pulse periods of the current flown into the drive circuit for operating the transmission, the pulse period T1 when the operation of the transmission is placed in a constant state becomes larger than the pulse period T2 when the operation of the transmission is not placed in a constant state. Accordingly, when the operation of the transmission is placed in a constant state, the number of switching times per unit time in the pulse width control section is decreased, so that the self-heating value of the pulse width control section based on the switching operation, namely, the self-heating value of the transmission ECU is suppressed. Therefore, if the transmission ECU is placed in an engine compartment, the temperature does not exceed the assurance temperature and thus damage to the semiconductor parts, etc., placed in the transmission ECU can be prevented.
According to a third aspect of the invention, a transmission electronic control unit is installed in a vehicle for controlling operation of a transmission installed in the vehicle. The transmission electronic control unit includes an operation detection section, a plurality of switching sections, and an energization control section. The operation detection section detects the operation state of the transmission. The plurality of switching sections is provided in a one-to-one correspondence with a plurality of drive circuits. The switching sections operate the transmission for connecting/shutting off energization of the corresponding drive circuits. The energization control section controls the operation of the plurality of switching sections separately so as to shut off energization of the drive circuits not required for the operation of the transmission.
In the third aspect of the invention, the operation detection section detects the operation state of the transmission and the energization control section separately controls connecting/shutting off the switching section provided in a one-to-one correspondence with the plurality of drive circuits for operating the transmission in response to output of the operation detection section. Accordingly, when the operation of the transmission is placed in a constant state, only the drive circuit required for holding the operation of the transmission in a constant state can be selected from among the drive circuits placed in the transmission ECU, only the switching section provided for the drive circuit required for operating the transmission can be brought into conduction, and the switching section provided for other drive circuits not required for operating the transmission can be shut off. That is, the number of the drive circuits brought into conduction by the switching section when the operation of the transmission is placed in a constant state can be lessened as compared with the number of the drive circuits brought into conduction by the switching section when the operation of the transmission is not placed in a constant state, so that the self-heating value of the transmission ECU is suppressed. Therefore, if the transmission ECU is placed in an engine compartment, the temperature does not exceed the assurance temperature and thus damage to the semiconductor parts, etc., placed in the transmission ECU can be prevented.
In the third aspect of the invention, the operation detection section may includes at least one selected from the group consisting of an accelerator opening sensor for detecting accelerator opening, an engine rotation sensor for detecting rotation speed of an engine, a speed sensor for detecting running speed of the vehicle, a turbine rotation sensor for detecting rotation speed of a turbine, a range sensor for detecting a working range of the transmission, a cruise sensor for detecting a cruise state of a state in which a run condition of the vehicle is set automatically, a navigation system, a laser radar, and a vehicle-installed camera.
In the above case, the operation detection section includes at least one member selected from the group consisting of an accelerator opening sensor, an engine rotation sensor, a speed sensor, a turbine rotation sensor, a range sensor, a cruise sensor, a navigation system, a laser radar, and a vehicle-installed camera. Thus, the operation detection section of the transmission is made up of the at least one member selected from among the members, so that operation detection of the transmission can be accomplished easily. A plurality of members selected from the group are used as the operation detection section of the transmission, whereby the control accuracy of the energization control section for executing the control operation in response to output of the operation detection section can be improved.